1. Field of the Invention
The present invention relates to an electronically-controlled throttle system which controls throttle opening angle electrically by driving a throttle valve by a motor or the like based on accelerator depression or the like.
2. Related Art
When throttle opening angle changes rapidly for vehicle acceleration or deceleration, engine torque changes greatly in a short time causing shock to a vehicle and uncomfortableness to vehicle passengers. JP-A 3-78542 and JPA-4-203251 disclose an electronic throttle control system for a vehicle which suppresses shock to a vehicle (vehicle shock) upon vehicle acceleration or deceleration. This system estimates required torque from accelerator depression and an engine rotation speed and filters the estimated torque by a filtering model matched to the vehicle to attenuate, by a predetermined attenuation rate, specified frequency components which are likely to cause vehicle shock. This filtering corrects the estimated torque in a direction to suppress vehicle shock. The system controls throttle opening angle in accordance with a target throttle opening angle calculated based on the corrected torque, thus suppressing vehicle shock at the time of rapid acceleration or deceleration.
This electronic throttle control system, however, calculates target throttle opening angle from corrected torque after estimating engine torque and correcting it by filtering estimated torque by the filtering model matched to the vehicle. Therefore, it not only makes complicated the control logic from the torque estimation to the target throttle opening angle calculation but also necessitates determination of matching constants for the filtering model varying from vehicle to vehicle. Determining such a complicated control logic and vehicle-specific filtering model requires an enormous amount of system development work, resulting in a longer development period and higher development cost.